The present invention relates generally to a method and a system for processing a video signal. More particularly, the invention relates to a method and system for processing an input video signal which is sampled at points of uniform phase so as to be vertically aligned on a screen.
When an analog input video signal is processed for conversion into a digital video signal in preparation for recording, reproduction, broadcast and so forth, it is considered good practice to use synchronization and sample gating signals to ensure that the sampling phases of the analog input video signal are aligned in predetermined relationships. For example, when interlacing screen lines by averaging the digital video signal values for screen pixels immediately above and below each interlaced pixel, it is essential that the sampling phases for every line on the screen be aligned to ensure accurate average values. In addition, when using elements such as a noise reducer, a comb filter or the like, the sampling phases, i.e. the position of sampled data in each line of the screen, must be vertically aligned.
Conventionally, a time base correction circuit (TBC) has been employed to match the sampling phases during conversion of an analog video signal into a digital video signal. Digital data sampling is performed on the output of the time base correction circuit.
In this case, the time base correction circuit converts the analog input video signal into a pulse train indicative of a fixed number of sampled video signal values between successive pulses of a synchronizing signal contained in the input video signal, and stores the sampled video signal values in a memory. Thereafter, a read-out clock signal is produced in phase with the sampling phase of the analog input video signal. The sampled data is read out from the memory synchronously with this clock signal to re-form the analog video signal. This processing by means of the time base correction circuit has been generally accepted as an effective way of removing jitter from the analog input video signal. However, since this process always requires analog-to-digital conversion and digital-to-analog conversion, it inevitably degrades the video signal content. Also, this conventional circuit construction is complicated and bulky due to the presence of the time base correction circuit.